As a device for measuring an inner diameter of a cylindrical member on non-contact basis, a non-contact type inner diameter measuring device is known, by which a laser beam is projected in a total circumferential direction, and an optical ring is formed on an inner surface of a cylindrical member, and an image of the optical ring is picked up, and a shape and a diameter of the optical ring are measured from the image.
Each of the Patent Document 1 and the Patent Document 2 discloses a non-contact type inner diameter measuring device, by which a laser beam is projected in a total circumferential direction, and an optical ring formed on an inner surface of a cylindrical member is picked up, and a shape and a diameter of the optical ring are measured from the image. In the inner diameter measuring device as described in each of the Patent Document 1 and the Patent Document 2, a cone mirror having a conical reflection surface is used as means for projecting a laser beam in a total circumferential direction, and the laser beam is reflected in a total circumferential direction by projecting the laser beam to a vertex of the cone mirror.
In a case where a cone mirror is used as means for projecting the laser beam in the total circumferential direction, it is necessary to make a center line of the cone mirror coincident with an optical axis of the laser beam. However, in the Patent Document 1 and the Patent Document 2, there is no special description about a method and a device to be used for making the center line of the cone mirror coincide with the optical axis of the laser beam.
To solve the problems as described above, it is an object of the present invention to provide an inner diameter measuring device, in which a laser beam is projected in a total circumferential direction by a cone mirror, and an optical ring is formed on an inner surface of a cylindrical member, and an inner diameter of the cylindrical member is measured according to the optical ring, and the inner diameter measuring device is provided with a core aligning mechanism for aligning a center line of the cone mirror with an optical axis of the laser beam.